For this type of apparatus, for example, there is proposed an apparatus in which a light emitting diode (LED) and a light receiving element are arranged around a medical tubing and in which hematocrit of a blood that flows in the medical tubing is measured from a light receiving signal (refer to Patent Literature 1). Alternatively, there is proposed an apparatus configured to apply laser light to a tubing in which a blood flows, and configured to correct a blood flow volume, which is calculated from a Doppler shift of the laser light, on the basis of a blood concentration calculated from an amount of light received by the light receiving element (refer to Patent Literature 2).